Hmm. Probably have to say 'crop factor'. Low weight is handy, but I have smaller point-n-shoots for that. The FT-1 adapter gives me unique capabilities for shooting wildlife. Stick a 300F4 on there and I have effective 810F4 that I can easily carry (and pack, and afford). Stick an 80-400g on there, and I have even more reach, plus VR and zoom.